Increasing demand worldwide for food production, especially in less developed countries, has sharpened interests in developing alternative sources of nutritionally significant proteins. Simultaneously, awareness has been focused more toward utilizing traditional by-products from the food industry for obtaining these new ingredients. In short, the food industry has, in recent years, focused on utilizing traditional food sources more fully and efficiently.
Whey is an ubiquitous liquid by-product obtained during the cheesemaking process. Raw whey contains highly nutritive proteins, albeit at relatively low concentrations. The high cost of current methods used to isolate these proteins has resulted in whey being a highly-underutilized source of nutritionally significant proteins.
In 1997, the world production of milk was estimated to be 471 million metric tons. Worldwide total production of cheese in 1997 was approximately 13 million metric tons. While no precise figures are available on the quantity of liquid whey produced, based upon the known total output of cheese and casein, an estimated 118 million metric tons of liquid whey was produced worldwide in 1997. This amount of raw liquid whey is equivalent to approximately 7 million metric tons of whey solids. Only about 62% of the worldwide production of whey is utilized for any purpose (food-related or otherwise). The remaining 38% is discarded as waste. In 1995, total whey powder production in the United States was 648,000 metric tons, with a production of 108,000 metric tons of WPC.
Thus, there remains a long felt and unmet need to utilize the nutritive components found in whey. For example, the proteins found in whey can be used as nutritional ingredients in milk that has been altered for infant consumption. These proteins can also be used as dietary supplements and in various food products. For example, whey proteins can be used as functional ingredients in foods, such as in the use of texture or consistency modifiers. emulsifiers, and the like. Whey proteins have excellent functional properties, and the functionality of these various proteins is related directly to their composition. Thus, an efficient and economic method to fractionate whey into its component proteins would result in the more complete utilization of whey as a food source.
A basic requirement for utilizing whey as a source of proteins is a method that isolates the whey proteins in good quality and low cost. For protein utilization in particular, not only must the proteins be isolated with good microbiological properties, but also their physical and chemical qualities must also be preserved. However, for the majority of food applications that would use proteins from whey, it is necessary to obtain these proteins in a more concentrated form. It may also be necessary to separate specific proteins. Several processes are now known for obtaining concentrated proteins or protein fractions from whey. These methods include ultrafiltration, ion exchange, electro dialysis, reverse osmosis, heat precipitation, and precipitation by complexation, among other methods. However, all of these methods entail certain insurmountable barriers, such as economics, time, or ease of use.
At present, the most widely used method of whey protein concentration is via ultrafiltration. Other methods of concentration often require high power energy consumption, have relatively low productivity, result loss of protein functionality as a result of denaturation of the proteins, and sometimes require additional purification steps.
Whey contains water, lactose, proteins, minerals, and residual fat. Lactose is the major component, with only about 6% of the total lactose found in milk being retained in the cheese curd during the cheesemaking process. Whey also has a high mineral content, which can be as much as 70% of the total whey protein weight. Conventionally, whey is used in the manufacture of certain kinds of cheese, such as ricotta. Other conventional uses are field spraying, animal feeding, alcohol production, drying for food use, wine and drink manufacture, and production of other components, such as lactose, yeast biomass, and proteins.
The term whey proteins per se refers to the milk proteins that remain soluble at pH 4.6 and at a temperature of 20° C. See, Eigel et al. (1984) J. Dairy Sci. 67:1599-1631. In the 1950's, the composition of whey was generalized as containing “true protein” and “non-protein nitrogen.” See, for example, Lampert, L. M. (1965) Modern Dairy Products, Chemical Publishing Company, Inc., New York, N.Y. According to the classical method, the true proteins were divided into “globulins” and “albumins.” According to this definition, the “lactalbumin” fraction of the whey contains proteins that are soluble in neutral, one-half saturated ammonium sulphate or saturated magnesium sulphate. Despite the name “lactalbumin,” this fraction contains up to 16% β-lactoglobulin. Thus, the use of the term lactalbumin for this purpose is incorrect because the name lactalbumin is related to a specific protein. In the ensuing years, however, new technologies were devised that enabled the fractionation of α-lactalbumin, β-lactoglobulin, lactoferrin, lactoperoxidase, immunoglobulins, and other minor parts from whey. See, for example, Fox, P. F. (1992) Advanced Dairy Chemistry—Vol. 1: Proteins, Vol. 1, Elsevier Applied Science, London, England.
Xanthan gum is a high molecular weight polysaccharide produced commercially using the microorganism xanthomonas campestris in a controlled fermentation process. At the end of fermentation, the gum is precipitated from the culture medium using isopropyl alcohol, dried, milled, and packaged. The dominant hexose units in the polysaccharide structure are D-glucose and D-mannose, along with D-glucuronic acid. Xanthan gum can be purchased from a number of international suppliers, including Degussa, which sells xanthan gum under the brand names SATIAXANE and ACTIGUM. Jungbunzlauer, of Geneva, Switzerland, also sells xanthan gum in industrial quantities.
Xanthan gum can be dispersed in hot or cold water, resulting in a viscous, non-thixotropic, opalescent solution. The final pH of a xanthan gum solution at approximately 0.1 to 1.0 percent concentration is approximately 6 to 7. An important characteristic of xanthan gum is that it is acid resistant. It can be dispersed directly into acidic solutions, without significant viscosity changes.
Xanthan gum has a molecular weight that is greater than 2 million Daltons. The polymer backbone of xanthan gum consists of 1,4-linked β-D-glucuronic acid, with D-glucose, D-mannose, and D-glucuronic acid residues. Each repeating block in xanthan gum contains 5 sugar units (2 glucose units, 2 mannose units, and 1 glucuronic acid unit). The final viscosity of a xanthan gum solution will depend on the gum concentration. However, high viscosity solutions occur at low xanthan concentration. Xanthan gum solutions are pseudo-plastic (i.e., sheer-thinning), meaning the viscosity of a xanthan gum solution will decrease as the sheer rate is increased. Pseudo-plasticity is an important property for the function of xanthan gum as a food modifier. For example, it allows suspensions and emulsions to be easily poured from a container due to the decreased viscosity caused by the increased sheer forces encountered when the liquid is poured. This decrease in viscosity is instantaneous and reversible. Another interesting aspect of xanthan gum solutions is that they have a practically constant viscosity at extreme temperature ranges (e.g., a 1% xanthan gum solution has an essentially constant viscosity at temperatures ranging anywhere from −18° C. to approximately 79° C.). Viscosity also remains essentially constant between pH 6 and pH 9, with only small changes in viscosity over the pH range from about pH 1 to about pH 11. In short, xanthan gum solutions make excellent food modifiers because of their high viscosity, high degree of pseudo-plasticity, high yield value, and extreme stability to heat and pH variation, in addition to high compatibility with salts, acids, bases, and enzymes.
Sodium carboxymethylcellulose (CMC) is a water soluble, linear, and long chain of polysaccharide having anionic characteristics. It is a chemically-modified natural gum. Cellulose is reacted with sodium hydroxide to yield alkylcellulose. The alkylcellulose is then treated with sodium monochloroacetate, thus resulting in carboxymethylcellulose. Uses for this polysaccharide are extensive, with particular importance in the food industry.
When characterizing CMC, the number of hydroxyl groups on each anhydroglucose unit of the cellulose backbone that is substituted with the carboxymethyl group is referred to as the “degree of substitution” (DS). Because there are three hydroxyl groups in each glucose unit, the maximum theoretical DS is three. In practice, however, this value is much lower. Commercial samples of CMC have DS values ranging from 0.4 to 1.2. Food grade CMC has DS values of approximately 0.9 or lower. The measurement “degree of polymerization” (DP) is related to the number of molecules in the polymer. In short, the greater the DP, the higher is the viscosity of the CMC solution. Food applications of CMC include thickening agents, suspension agents, stabilization agents, gelation agents, and flow modification agents. Perhaps the widest use of CMC is as a stabilizer in the manufacture of frozen dairy desserts such as ice cream, frozen custard, and instant frozen desserts. The CMC gives these products more consistent uniformity, extended shelf life, and improved tolerance to oscillating temperatures. In acidified and neutral milk beverages, CMC is an effective stabilizer, finding use in egg nog, milkshakes, infant formulas, and chocolate milk. It is also used in bakery products to control moisture uptake.